Reference marks #3 and #4. They were set during a survey check in 1971 when it was discovered that marks #1 and #2 were no longer there. (I read about this after I got back). Apparently the post for #1 and visibly broken rock for #2 are still identifiable. I didn't find them because they were more than twice as far from the BM as these two so I wasn't searching that far away after seeing these. (I think it's the first time I've seen a "No. 4")